Communication device, communication controlling method, and non-transitory computer-readable media

ABSTRACT

Provided are a communication device, a communication controlling method, and a non-transitory computer-readable medium storing a communication controlling program that each make it possible to grasp the condition of communication quality. A communication device ( 1 ) includes acquiring means ( 2 ) configured to acquire quality information concerning a burst error that has occurred in an optical communication line. The communication device ( 1 ) includes estimating means ( 3 ) configured to estimate a first index value based on the quality information acquired by the acquiring means ( 2 ), the first index value indicating a degree of influence of the burst error on communication quality in a first communication device.

TECHNICAL FIELD

The present disclosure relates to communication devices, communicationcontrolling methods, and non-transitory computer-readable media.

BACKGROUND ART

As described in Patent Literature 1, a burst error may occur incommunication carried out between two communication devices via atransmission line. Patent Literature 1 discloses a technique ofreproducing a burst error that has occurred in a transmission line.

There is known an optical communication system that communicates via anoptical communication line. In this optical communication system,generally a powerful error correction process is performed, and ascompared to a land-based communication system, the optical communicationsystem provides its end users with so-called error-free communication inwhich the error rate of transmitted or received data is extremely low.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application PublicationNo. 2018-116344

Non Patent Literature

Non Patent Literature 1: Jesse E. Simsarian, Young-Jin Kim, NakjungChoi, Catello Di Martino, Nishok N. Mohanasamy, Peter J. Winzer, andMarina Thottan. “Error Awareness in a Multi-Layer Transport NetworkOperating System,” Journal of Optical Communications and Networking,Vol. 10, Issue 3, February 2018.

Non Patent Literature 2: Yohei Hasegawa and Jiro Katto. “A TransmissionControl Protocol for Long Distance High-Speed Wireless Communications,”IEICE Trans. on Communication, Vol. E101-B, No. 4, April 2018.

Non Patent Literature 3: Neal Cardwell, Yuchung Cheng, C. Stephen Gunn,Soheil Hassas Yeganeh, and Van Jacobson. “BBR: Congestion-BasedCongestion Control,” ACM Queue, Vol. 14, Issue 5, December 2016.

SUMMARY OF INVENTION Technical Problem

In an optical communication system, for example, a large margin is setto a communication setting, such as a necessary signal-to-noise ratio(SNR) or an error correction process, in order to provide its end userswith error-free communication and a stable long-lasting service.

In recent years, communication service providers that managecommunication facilities and communication lines (communicationinfrastructure) in optical communication systems have diversified. Somecommunication service providers may be inclined to secure communicationcapacity of communication infrastructure by setting the acceptablecommunication quality in optical communication systems lower than thecommunication quality in error-free communication. The diversificationof communication service providers in the field of optical communicationsystems has made it necessary to take into consideration not only thecommunication quality but also the communication capacity ofcommunication infrastructure. Hence, in one possible scenario, acommunication service provider may run an optical communication systemin which, for example, a low margin is set to a communication setting inorder to increase the communication capacity. However, if a change ismade to a margin set to a communication setting, this makes it difficultto grasp the condition of communication quality provided to the users,and this situation may make it impossible for the communication serviceprovider to grasp the condition of communication quality appropriately.

To address the circumstances above, one object of the present disclosureis to provide a communication device, a communication controllingmethod, and a non-transitory computer-readable medium that each make itpossible to grasp the condition of communication quality.

Solution to Problem

A communication device according to the present disclosure includes:

acquiring means configured to acquire quality information concerning aburst error that has occurred in an optical communication line; and

estimating means configured to estimate a first index value based on thequality information, the first index value indicating a degree ofinfluence of the burst error on communication quality in a firstcommunication device.

A communication controlling method according to the present disclosureincludes:

acquiring quality information concerning a burst error that has occurredin an optical communication line; and

estimating a first index value based on the quality information, thefirst index value indicating a degree of influence of the burst error oncommunication quality in a first communication device.

A non-transitory computer-readable medium according to the presentdisclosure stores a communication controlling program that causes acomputer to execute:

acquiring quality information concerning a burst error that has occurredin an optical communication line; and

estimating a first index value based on the quality information, thefirst index value indicating a degree of influence of the burst error oncommunication quality in a first communication device.

Advantageous Effects of Invention

The present disclosure can provide a communication device, acommunication controlling method, and a non-transitory computer-readablemedium that each make it possible to grasp the condition ofcommunication quality.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example of a configuration ofa communication device according to an overview of some exampleembodiments.

FIG. 2 illustrates an example of a configuration of an opticalcommunication system according to a first example embodiment.

FIG. 3 is a diagram comparing a typical TCP scheme and ultra-high-speedTCP.

FIG. 4 illustrates a condition of data transmission and receptionbetween optical transmission devices.

FIG. 5 illustrates a relationship between an error rate and SNR in aplurality of modulation schemes.

FIG. 6 illustrates a condition of communication of a TCP scheme.

FIG. 7 is a flowchart illustrating an example of an operation of anoptical transmission device according to the first example embodiment.

FIG. 8 illustrates an example of a configuration of an opticalcommunication system according to a second example embodiment.

FIG. 9 illustrates an example of a hardware configuration of acommunication device and others according to some example embodiments.

EXAMPLE EMBODIMENT

Hereinafter, some example embodiments of the present disclosure will bedescribed with reference to the drawings. In the following descriptionand drawings, omissions and simplifications are made, as appropriate, tomake the description clearer. In the drawings, identical elements aregiven identical reference characters, and their repetitive descriptionwill be omitted, as necessary.

Examinations Leading to Example Embodiments

As described above, with the diversification of service providersproviding communication infrastructure, some communication serviceproviders may hope to increase communication capacity in opticalcommunication systems. In one possible scenario, such a communicationservice provider may increase communication capacity by, for example,reducing a margin set to a communication setting, such as necessary SNRor an error correction process (forward error correction (FEC)).

Non Patent Literature 1 indicates that reducing a margin set to acommunication setting causes a non-frequent burst error. Such a bursterror is a post-FEC burst error. Non Patent Literature 1 discloses arelationship between, for example, a quality value such as SN ratio anda Post-FEC bit error rate (BER) in an optical communication andindicates that a burst error occurs non-frequently when the qualityvalue has become worse than a predetermined value.

Meanwhile, a communication service provider that wants to increasecommunication capacity may achieve this by increasing communicationchannels to increase communication capacity, but an increase incommunication channels may cause a burst error. Moreover, a burst errormay occur in response to a change in the voltage at a communication linecaused by, for example, lightning, an earthquake, or the like.

In this manner, communication capacity can be increased by reducing acommunication setting margin, a margin set to a communication setting.However, such reduction causes a burst error non-frequently, and thus acommunication setting margin needs adjusting with a grasp of thecondition of communication quality including the degree of influence ofa burst error on users. Accordingly, the inventor has found that acommunication service provider can grasp the condition of communicationquality by estimating an index value indicating the degree of influence,on users, of a burst error that occurs when a communication settingmargin has been changed.

Overview of Example Embodiments

FIG. 1 is a block diagram illustrating an example of a configuration ofa communication device according to an overview of some exampleembodiments. A communication device 1 partly constitutes an opticalcommunication system and may be, for example, an optical transmissiondevice or a network monitoring device that monitors and controls theoptical communication system. The communication device 1 includes anacquiring unit 2 and an estimating unit 3.

The acquiring unit 2 acquires quality information concerning a bursterror that has occurred in an optical communication line. The opticalcommunication line is, for example, a submarine cable. The qualityinformation may include a communication round-trip time between opticaltransmission devices connected to an optical communication line 16 and aburst error time of a burst error. The communication round-trip time maybe a round-trip time (RTT). Herein, a plurality of pieces of data aretransmitted from an optical transmission device 20 to an opticaltransmission device 30, and thus the communication round-trip time maybe an average of RTTs between the optical transmission devices connectedto the optical communication line 16. The quality information mayinclude a first error rate in the optical communication line. The firsterror rate may be BER or a frame error rate (FER).

Based on the quality information acquired by the acquiring unit 2, theestimating unit 3 estimates a first index value indicating the degree ofinfluence of a burst error on the communication quality in a firstcommunication device. The first communication device may be an end userterminal managed by an end user or a relay device between an end userterminal and an optical transmission device.

The communication device 1, configured as described above, estimates thefirst index value, which indicates the degree of influence of a bursterror on the communication quality in the first communication device,based on the quality information concerning the burst error. Acommunication service provider that operates the optical communicationsystem can grasp the condition of communication quality based on thefirst index value. Accordingly, the communication device 1 according toan example embodiment makes it possible to grasp the condition ofcommunication quality by estimating the first index value.

First Example Embodiment

Hereinafter, a first example embodiment will be described with referenceto the drawings.

<Example of Configuration of Optical Communication System>

With reference to FIG. 2 , an example of a configuration of an opticalcommunication system 100 according to the first example embodiment willbe described. FIG. 2 illustrates an example of a configuration of anoptical communication system according to the first example embodiment.The optical communication system 100 includes a terminal device 10 andoptical transmission devices 20 and 30.

The terminal device 10 is, for example, a communication device providedon land. The terminal device 10 may be, for example but not limited to,an end user terminal managed by an end user or a relay device providedbetween an end user terminal and the optical transmission device 20. Inthe following description, the terminal device 10 is an end userterminal.

The terminal device 10 is connected to the optical transmission device20 via a circuit 15 and communicates with the optical transmissiondevice 20 via the circuit 15. The circuit 15 is, for example, an accesscircuit. The circuit 15 may be referred to as a communication linebetween the terminal device 10 and the optical transmission device 20.

The optical transmission devices 20 and 30 are communication devicesthat are connected to and communicate with each other via an opticalcommunication line 16, which is a submarine cable constituted, forexample, by optical fibers. The optical transmission devices 20 and 30each convert an optical signal transmitted or received via the opticalcommunication line 16 to an electric signal to be transmitted orreceived via the circuit 15 or a circuit (not illustrated) connected tothe optical transmission device 30. Moreover, the optical transmissiondevices 20 and 30 each convert an electric signal transmitted orreceived via the circuit 15 or a circuit (not illustrated) connected tothe optical transmission device 30 to an optical signal to betransmitted or received via the optical communication line 16.

The optical transmission devices 20 and 30 support a wavelength divisionmultiplexing (WDM) scheme and each transmit data to be transmitted orreceived via the optical communication line 16 to the opposing opticaltransmission device via a plurality of communication channels of aplurality of wavelength bands. Each communication channel may bereferred to as an optical spectrum.

The optical transmission device 20 and the optical transmission device30 communicate via a TCP scheme having higher error resistance than atypical TCP Reno scheme. The optical transmission device 20 and theoptical transmission device 30 execute a retransmission process via aTCP scheme having higher error resistance than a typical TCP Renoscheme, if an error has occurred in communication in the opticalcommunication line 16.

Non Patent Literatures 2 and 3 propose a TCP scheme having higher errorresistance than a TCP Reno scheme, which is a typical transmissioncontrol protocol (TCP) scheme, and capable of achieving high-speedcommunication. Non Patent Literature 2 proposes, as a TCP scheme havinghigh error resistance and capable of achieving high-speed communication,a transmission control protocol-free-space optical communications(TCP-FSO) scheme that is capable of achieving a data transmissionthroughput of higher than 10 Gbps. Non Patent Literature 3 as wellproposes a TCP scheme having higher error resistance than a typical TCPscheme. The TCP schemes disclosed in Non Patent Literatures 2 and 3 maybe referred to as an ultra-high-speed TCP scheme since these schemes arecapable of achieving high data transmission throughput.

FIG. 3 is a diagram comparing a typical TCP scheme and ultra-high-speedTCP. The horizontal axis in FIG. 3 indicates a link speed andcorresponds to communication capacity. The vertical axis indicates userthroughput. The dashed-dotted line shows Post-FEC BER. The dotted lineshows a relationship between the throughput and communication capacityof the typical TCP scheme. The solid line shows a relationship betweenthe user throughput and communication capacity of the ultra-high-speedTCP scheme disclosed in Non Patent Literatures 2 and 3.

The section circled by a dotted line in FIG. 3 shows the best userthroughput in the typical TCP scheme. The section circled by a solidline in FIG. 3 shows the best user throughput in the ultra-high-speedTCP scheme. As illustrated in FIG. 3 , the communication capacity heldwhen the user throughput is at its best is greater in theultra-high-speed TCP scheme than in the typical TCP scheme. Moreover,the user throughput does not fall even with an increase in Post-FEC BERin the ultra-high-speed TCP scheme, and the communication capacity canbe ensured while increasing the user throughput until it reaches thesection circled by the solid line. In this manner, the ultra-high-speedTCP scheme disclosed in Non Patent Literatures 2 and 3 can increase theuser throughput and communication capacity than the TCP Reno scheme, thetypical TCP scheme, even with a rise in Post-FEC BER. Therefore, theoptical transmission devices 20 and 30 execute a retransmission processby use of the TCP scheme disclosed in Non Patent Literatures 2 and 3 andhaving higher error resistance than the typical TCP Reno scheme. Thisconfiguration allows the optical transmission devices 20 and 30 toincrease communication capacity of the optical communication line 16.

The description continues with reference back to FIG. 2 . In response toproperly receiving data transmitted or received via the opticalcommunication line 16, the optical transmission devices 20 and 30 eachtransmit acknowledgement (ACK) to its opposing optical transmissiondevice. If the optical transmission devices 20 and 30 fail to receiveacknowledgement for data transmitted or received via the opticalcommunication line 16, the optical transmission devices 20 and 30retransmit the data for which they have failed to receiveacknowledgement.

The optical transmission device 20 corresponds to the communicationdevice 1. The optical transmission device 20 transmits data transmittedfrom the terminal device 10 to a terminal device (not illustrated)opposing the terminal device 10 via the optical communication line 16and the optical transmission device 30. The optical transmission device20 receives data transmitted to the terminal device 10 and transmits thereceived data to the terminal device 10.

The optical transmission device 30 transmits data transmitted from aterminal device (not illustrated) opposing the terminal device 10 to theterminal device 10 via the optical communication line 16 and the opticaltransmission device 20. The optical transmission device 30 receives datatransmitted to a terminal device (not illustrated) opposing the terminaldevice 10 and transmits the data to the terminal device (notillustrated) opposing the terminal device 10.

<Example of Configuration of Optical Transmission Device>

Next, an example of a configuration of the optical transmission device20 will be described. The optical transmission device 20 includes aretransmission process unit 21, an acquiring unit 22, an estimating unit23, a controlling unit 24, and an output unit 25.

The retransmission process unit 21 executes a retransmission process ifan error occurs in communication in the optical communication line 16.The retransmission process unit 21 executes a retransmission process bycommunicating via an ultra-high-speed TCP scheme having higher errorresistance than a typical TCP Reno scheme.

The retransmission process unit 21 transmits data to the opticaltransmission device 30 via the optical communication line 16. Theretransmission process unit 21 receives acknowledgement (ACK) for thisdata from the optical transmission device 30. In response to receivingthe acknowledgement (ACK), the retransmission process unit 21 transmitsanother piece of data following the aforementioned data. Meanwhile, ifthe retransmission process unit 21 receives no acknowledgement (ACK),the retransmission process unit 21 retransmits the data for which theretransmission process unit 21 has received no acknowledgement. Theretransmission process unit 21 receives data from the opticaltransmission device 30 via the optical communication line 16. If theretransmission process unit 21 has received this data properly, theretransmission process unit 21 transmits ACK to the optical transmissiondevice 30.

The acquiring unit 22 includes, for example, an optical spectrummeasuring device, such as an optical channel monitor (OCM) or an opticalspectrum analyzer. The acquiring unit 22 acquires quality informationconcerning a burst error that occurs in communication in the opticalcommunication line 16. The quality information includes RTT indicating acommunication round-trip time between the optical transmission devices20 and 30 connected to the optical communication line 16, a burst errortime in which a burst error has occurred, and an error rate in theoptical communication line 16.

The quality information may further include the number of users whocommunicate via the optical communication line 16 and SNR indicating anoptical signal quality in the optical communication line 16. The opticalsignal quality may be an optical signal-to-noise ratio (OSNR).

The error rate may be BER or FER. Herein, a Post-FEC burst error isexpected to occur non-frequently, and thus BER and FER are expected tohave substantially the same value. Therefore, the acquiring unit 22 mayacquire BER or FER. A variable representing the error rate in theoptical communication line 16 is defined as P. In the present exampleembodiment described herein, the error rate is BER.

Now, RTT and the burst error time will be described with reference toFIG. 4 . FIG. 4 illustrates a condition of data transmission andreception between the optical transmission devices. The solid lines andthe dotted lines show data transmitted from the optical transmissiondevice 20 on the data transmitting end to the optical transmissiondevice 30 on the data receiving end. The solid lines show datatransmitted from the optical transmission device 20 and receivedproperly by the optical transmission device 30. The dotted lines showdata transmitted from the optical transmission device 20 and havingfailed to be received properly by the optical transmission device 30.The dashed-three-dotted lines each show acknowledgement sent from theoptical transmission device 30. Herein, the optical transmission device30 also serves as a device on the transmitting end, and the opticaltransmission device 20 also serves as a device on the receiving end.

RTT is the length of time between the transmission time when data istransmitted from the optical transmission device 20 to the opticaltransmission device 30 and the reception time when acknowledgement forthis data is received by the optical transmission device 20. When thelength of time from the transmission of data by the optical transmissiondevice 20 to the arrival of this data at the optical transmission device30 is defined as D, RTT can be expressed by 2 D. The acquiring unit 22monitors data transmitted to the optical transmission device 30 andacquires RTT based on the length of time from the transmission time ofthe data to the reception time of acknowledgement for this data.

Herein, the acquiring unit 22 may hold position informationcorresponding to the IP addresses of the optical transmission devices 20and 30, identify the positions of the optical transmission devices 20and 30 based on the IP addresses in data transmitted from the opticaltransmission device 20 to the optical transmission device 30, anddetermine RTT by calculating the distance between the positions.

A burst error time is the duration of a burst error that has occurredwithin an RTT, and a variable representing a burst error time is definedas L. A plurality of burst errors can occur within an RTT, and thus aburst error time is the total duration of a plurality of burst errorsthat have occurred within an RTT. In FIG. 3 , a series of dotted linesappear in the section indicated by the rectangle, and this indicatesthat burst errors have occurred. The acquiring unit 22 acquires, as aburst error time, the total length of time in which a series of datatransmitted to the optical transmission device 30 has failed to bereceived properly. Since a plurality of pieces of data are transmittedfrom the optical transmission device 20 to the optical transmissiondevice 30, the burst error time is an average of the total duration ofburst errors with respect to the plurality of pieces of data.

The estimating unit 23 estimates an index value indicating the degree ofinfluence of a burst error on communication quality in the terminaldevice 10, based on quality information acquired by the acquiring unit22. The index value includes a user proportion indicating the proportionof the number of users for whom the communication quality deteriorateswith respect to the number of users who communicate via the opticalcommunication line 16, a delay time in the terminal device 10, and theprobability of failing to satisfy a delay quality index value pertainingto a delay time required for communication in an optical communicationline.

The user proportion can also be explained as the proportion of thenumber of users for whom the delay time deteriorates due to aretransmission process with respect to the number of users whocommunicate via the optical communication line 16. A user for whom thedelay time deteriorates due to a retransmission process cannot use thecommunication circuit during the retransmission process, and thus theuser proportion can also be explained as the proportion of users who areunable to use the communication circuit in a certain period of time.

The terminal device 10 is an end user terminal according to the presentexample embodiment, and thus a delay time in the terminal device 10 is adelay time at an end user and may be referred to as a user delay time.The delay quality index value is an index value pertaining to a delaytime that a communication service provider managing the opticalcommunication line 16 requires for communication in the opticalcommunication system. The probability of failing to satisfy the delayquality index value can also be stated as the probability of failing tomaintain communication quality and may thus be referred to as theprobability of quality deterioration. Herein, the estimating unit 23estimates the index value described above with an assumption that noisein the optical communication line 16 is additive white Gaussian noise(AWGN).

The estimating unit 23 estimates the user proportion based on RTT and aburst error time acquired by the acquiring unit 22. Herein, when avariable representing the user proportion is defined as A, the userproportion can be calculated through the following equation (1).Therefore, the estimating unit 23 estimates the user proportion by useof the equation (1).

[Math. 1]

A=L/D

If A<A′  (1)

In the above, A is the user proportion, L is a burst error time, D ishalf the duration of RTT, and A′ is a target threshold. While D in theequation (1) is half the duration of RTT, the variable D may be replacedby RTT.

Whereas a typical error rate is expressed by the number of errors/thenumber of pieces of communication data, the above user proportion is theprobability with which user communication is carried out during a bursterror. For example, if an average burst error time L is 10 ms and acommunication round-trip time D is 30 ms, A turns out to be 10 ms/30ms=⅓, which is high relative to a typical error rate. In this manner,the estimating unit 23 can detect an influence of a burst error withhigh sensitivity by obtaining the variable A indicating the userproportion by use of the above equation (1). In other words, since theestimating unit 23 calculates the degree of influence of a burst errorwith high sensitivity, the use of the user proportion calculated throughthe above equation (1) makes it possible to provide users with a stablecommunication service.

The estimating unit 23 estimates a delay time in the terminal device 10based on RTT and BER acquired by the acquiring unit 22. In other words,the estimating unit 23 estimates a user delay time based on RTT and BER.Herein, when a variable representing the delay time in the terminaldevice 10 is defined as D_(user), the delay time in the terminal device10 can be calculated through the following equation (2). The estimatingunit 23 estimates a delay time in the terminal device 10 by use of theequation (2).

[Math.2] $\begin{matrix}{{D_{user} = {D + {\sum\limits_{i = 1}^{\infty}{{DP}^{i}\left( {1 - P} \right)}}}}{{{If}D_{user}} < D^{\prime}}} & (2)\end{matrix}$

In the above, D_(user) is the delay time in the terminal device 10, D ishalf the duration of RTT, P is BER in the optical communication line 16,and D′ is a target threshold. While the variable D in the equation (2)is a variable indicating half the duration of RTT, the variable D may bereplaced by RTT.

In the above equation (2), i represents the number of instances ofretransmission process, and the second term on the right-hand siderepresents a delay time with a retransmission process taken intoconsideration. The estimating unit 23 estimates a delay time in theterminal device 10 with a retransmission process taken intoconsideration.

The estimating unit 23 estimates the probability of failing to satisfythe delay quality index value in the terminal device 10 based on RTT,BER, and the delay quality index value acquired by the acquiring unit22. In other words, the estimating unit 23 estimates the probability ofquality deterioration based on RTT, BER, and the delay quality indexvalue.

Herein, when a variable representing the probability of failing tosatisfy the delay quality index value is defined as P_(DF), theprobability of failing to satisfy the delay quality index value can becalculated through the following equation (3). The estimating unit 23estimates the probability of failing to satisfy the delay quality indexvalue by use of the equation (3).

[Math.3] $\begin{matrix}{{P_{DF} = {{P^{({n + 1})}\left( n \right.} = {\frac{D_{SLA}}{D} \geq \left. 2 \right)}}}{{{If}P_{DF}} < P^{\prime}}} & (3)\end{matrix}$

In the above, P_(DF) is the probability of failing to satisfy the delayquality index value, D is half the duration of RTT, P is BER in theoptical communication line 16, D_(SLA) is the delay quality index value,and P′ is a target threshold. While the variable D in the equation (3)is a variable indicating half the duration of RTT, the variable D may bereplaced by RTT.

In the equation (3), n represents the number of instances ofretransmission in retransmission process executed in the opticalcommunication line 16, and this number is determined based on the delayquality index value. If a retransmission process is executed n timesbased on the delay quality index value D_(SLA), P_(DF) can be stated asthe probability of quality deterioration with which communicationquality will no longer be maintained. As described above, sinceP_(DF)=P^((n+1)), the probability of quality deterioration is very low,and an influence on the average delay time is also small. In otherwords, a communication service provider can operate the opticalcommunication system with a smaller margin by use of the above equation(3). In other words, even though the error rate is not eliminated, acommunication service provider can operate the optical communicationsystem with increased communication capacity.

The controlling unit 24 changes a communication setting in the opticalcommunication line 16 by use of the user proportion estimated by theestimating unit 23. The controlling unit 24, by use of the userproportion estimated by the estimating unit 23, changes the modulationscheme in communication in the optical communication line 16 and adjustsa communication setting margin.

Moreover, the controlling unit 24 may, by further use of the number ofusers who communicate via the optical communication line 16 and SNRindicating the optical signal quality, change the modulation scheme incommunication in the optical communication line 16 and adjust acommunication setting margin.

A plurality of modulation schemes can be used in communication in theoptical communication line 16. Examples of such modulation schemes usedin communication in the optical communication line 16 include BinaryPhase shift Keying (BPSK), Quadrature Phase shift Keying (QPSK),8-Quadrature Amplitude Modulation (QAM), 16-QAM, 32-QAM, 64-QAM,128-QAM, or 256-QAM.

In short-duration communication, the communication speed (throughput)decreases for user communication that has experienced a burst error dueto a retransmission process, and thus the utilization rate of thecommunication circuit may decrease during a burst error. The controllingunit 24, taking the user proportion into consideration, adjusts acommunication setting margin so that the total B_(EST) of thecommunication speed of users for whom no retransmission process isperformed momentarily does not fall far below the circuit speed B_(MOD)of the optical communication line 16.

Herein, when the number of users who communicate via the opticalcommunication line 16 is represented by U and the user communicationspeed is represented by B_(TCP), B_(EST) can be expressed as in theequation (4). The controlling unit 24 calculates B_(EST) by use of theequation (4). Herein, the variable A represents the user proportionestimated by the estimating unit 23, and the variable U represents thenumber of users acquired by the acquiring unit 22.

[Math. 4]

B _(EST)=(1−A)×U×B _(TCP)   (4)

An ultra-high-speed TCP scheme is adopted in the optical transmissiondevices 20 and 30, and the user communication speed B_(TCP) can beexpressed as in the following equation (5).

[Math.5] $\begin{matrix}{B_{TCP} = {\frac{W}{D\log(W)}{\log\left( \frac{1}{P} \right)}}} & (5)\end{matrix}$

In the above, D is a communication round-trip time, W is a buffer sizeof a buffer that temporarily holds data for performing communication ofa TCP scheme, and P is BER. The variable W can be acquired in advance bythe controlling unit 24 from its host device.

Herein, if a typical TCP scheme is adopted in the optical transmissiondevices 20 and 30, the user communication speed B_(TCP) can be expressedas in the following.

[Math.6] $B_{TCP} = \frac{V}{D\sqrt{P}}$

In the above, D is a communication round-trip time, P is BER, and V is aconstant. Herein, the constant V is, for example, 0.866.

A communication setting margin can be changed by changing themulti-value level of a multi-level modulation scheme, where themulti-value level indicates the number of states allowing transmissionin one communication symbol. When a variable representing themulti-value level is M, a variable representing the communication speedin a multi-level modulation scheme is B_(MOD), and a variablerepresenting the communication speed of BPSK, which is a modulationscheme indicating two states with one symbol, is B_(B), B_(MOD) can beexpressed as in the following equation (6). Herein, the variable Mrepresenting the multi-value level can be from 4 to 4096. Thecontrolling unit 24 can achieve the above by setting the variable B_(B)in advance. The controlling unit 24 determines the modulation schemebased on the variable M representing the multi-value level and can thushold the variable M representing the multi-value level, which will bedescribed later.

[Math. 7]

B _(MOD)=log₂ M×B _(B)   (6)

Now, a relationship between Post-FEC BER and SNR in a plurality ofmodulation schemes will be described with reference to FIG. 5 . FIG. 5illustrates a relationship between an error rate and SNR in a pluralityof modulation schemes. The horizontal axis in FIG. 5 indicates SNR, andthe vertical axis indicates Post-FEC BER. As illustrated in FIG. 5 ,when Post-FEC BER is identical, higher SNR is required as themulti-value level of a modulation scheme is higher. In this manner, ahigher multi-value level requires communication of higher SNR.

A variable P_(MOD) representing the error rate in a modulation schemewith respect to the variable M representing the multi-value level can beexpressed as in the following equation (7).

[Math.8] $\begin{matrix}{P_{MOD} = {\frac{4}{k}{\left( {1 - \frac{1}{\sqrt{M}}} \right) \times \frac{1}{2}}{erfc}\left( \sqrt{\frac{3{k \times {SNR}}}{M - 1}} \right)}} & (7)\end{matrix}$

In the above, k is a symbol length of a communication signal, SNR is anoptical signal quality in the optical communication line 16, and erfc isa complementary error function. Herein, the complementary error functionerfc can be expressed by the following equation (8).

[Math.9] $\begin{matrix}{{{erfc}(x)} = {\frac{2}{\sqrt{2}}{\int_{x}^{\infty}{e^{- t^{2}}{dt}}}}} & (8)\end{matrix}$

When B_(EST) is smaller than B_(MOD), the controlling unit 24 determinesa new multi-value level M_(i+1) by lowering the multi-value level tolower than the current multi-value level M_(i). In other words, thecontrolling unit 24 sets the multi-value level to M_(i+1)=M_(i−1).

The controlling unit 24 changes the modulation scheme from a modulationscheme that can be used in communication in the optical communicationline 16 described above to a modulation scheme corresponding to M_(i+1).The controlling unit 24 changes a communication setting margin bychanging the modulation scheme. By changing the modulation scheme, thecontrolling unit 24 achieves communication in which users are lesslikely to sense a decrease in communication quality.

Meanwhile, when at least one of a burst error time or P_(MOD) is smallerthan, for example, a target threshold, the controlling unit 24determines a new multi-value level M_(i+1) by raising the multi-valuelevel to higher than the current multi-value level M_(i). In otherwords, the controlling unit 24 sets the multi-value level toM_(i+1)=M_(i+1).

The controlling unit 24 changes the modulation scheme from a modulationscheme that can be used in communication in the optical communicationline 16 described above to a modulation scheme corresponding to M_(i+1).The controlling unit 24 changes a communication setting margin bychanging the modulation scheme. By changing the modulation scheme, thecontrolling unit 24 provides users with a high-speed communicationservice.

Herein, the controlling unit 24 may change a communication settingmargin if the user proportion has exceeded a target threshold A′ of theuser proportion. For example, if the user proportion has exceeded A′,the controlling unit 24 may change the modulation scheme to a modulationscheme corresponding to a multi-value level that is smaller than thecurrent multi-value level by one. Meanwhile, if the user proportion is asufficiently small value, such as 0.1, for example, the controlling unit24 may change the modulation scheme to a modulation scheme correspondingto a multi-value level that is greater than the current multi-valuelevel by one. The controlling unit 24 provides users with a high-speedcommunication service by changing the modulation scheme and adjusting acommunication setting margin. In other words, the controlling unit 24can provide users with a high-speed communication service even if BER ofthe optical communication line 16 has become higher than, for example,10⁻¹² with a communication setting margin that can cause a burst error.

The controlling unit 24 changes a communication setting so that a bursterror time does not exceed RTT. FIG. 6 illustrates a condition ofcommunication of a TCP scheme. FIG. 6 shows that the burst error timehas exceeded the congestion window (cwnd) used in a TCP scheme.

In a TCP scheme, retransmission time out (RTO) is provided as a timerrelated to a retransmission process. As illustrated in FIG. 6 ,retransmission is carried out triggered by RTO upon the burst error timeexceeding the congestion window. When retransmission triggered by RTO iscarried out, a retransmission process is executed after a length of timecorresponding to the RTO has passed from the data transmission starttime. In other words, a retransmission process ceases to be performeduntil a length of time corresponding to the RTO passes from the datatransmission start time. This case produces a duration in which no datais transmitted and limits the amount of data to be transmitted, and thisleads to a large decrease in performance. Therefore, the controllingunit 24 performs control so that a burst error time does not exceed RTT.Specifically, the controlling unit 24 performs control so that a bursterror time does not exceed RTT and keeps the throughput andcommunication capacity from decreasing by preventing retransmissiontriggered by RTO.

The controlling unit 24 changes an interleave length in an errorcorrection process (FEC) so that a burst error time does not exceed RTT.Specifically, the controlling unit 24 performs control so that a bursterror time does not exceed RTT by setting a short interleave in FEC. Thecontrolling unit 24 can increase the user throughput and communicationcapacity by changing an FEC setting as in adjusting the interleavelength.

The output unit 25 outputs an index value estimated by the estimatingunit 23 and indicating the degree of influence of a burst error oncommunication quality in the terminal device 10. As described above, anindex value includes the user proportion, a delay time in the terminaldevice 10, and the probability of failing to satisfy a delay qualityindex value. The output unit 25 outputs the user proportion, a delaytime in the terminal device 10, and the probability of failing tosatisfy a delay quality index value.

The output unit 25 may output the index value by transmitting the indexvalue to a communication terminal used by a manager or an operator ofthe optical communication line 16. Alternatively, the output unit 25 mayoutput the index value by transmitting the index value to acommunication service provider managing the optical communication line16. Alternatively, the output unit 25 may output the index value bytransmitting the index value to a network monitoring device (notillustrated) that monitors the entire network in the opticalcommunication system 100. Alternatively, the output unit 25 may outputthe index value to a display device included in the optical transmissiondevice 20.

<Example of Operation of Optical Transmission Device>

Next, with reference to FIG. 7 , an example of an operation of theoptical transmission device 20 according to the first example embodimentwill be described. FIG. 7 is a flowchart illustrating an example of anoperation of the optical transmission device according to the firstexample embodiment. The example of the operation illustrated in FIG. 7is executed upon the start of the optical transmission device 20. Inaddition, the example of the operation illustrated in FIG. 7 is executedwhen a communication service provider has made a change to acommunication setting. Herein, the example of the operation illustratedin FIG. 7 may be executed periodically or non-periodically.

The acquiring unit 22 acquires quality information concerning a bursterror that has occurred in communication in the optical communicationline 16 (step S1). The acquiring unit 22 acquires RTT indicating acommunication round-trip time between the optical transmission devices20 and 30 connected to the optical communication line 16, a burst errortime in which a burst error has occurred, and BER indicating an errorrate in the optical communication line 16. The acquiring unit 22 mayfurther acquire the number of users who communicate via the opticalcommunication line 16 and SNR in the optical communication line 16.

The estimating unit 23 estimates the user proportion indicating theproportion of the number of users for whom communication qualitydeteriorates with respect to the number of users who communicate via theoptical communication line 16, based on the RTT and the burst error timeacquired by the acquiring unit 22 (step S2). The estimating unit 23estimates the user proportion based on the RTT and the burst error timeby use of the equation (1).

The estimating unit 23 estimates a user delay time based on the RTT andthe BER acquired by the acquiring unit 22 (step S3). The estimating unit23 estimates the delay time in the terminal device 10 based on the RTTand the BER by use of the equation (2).

The estimating unit 23 estimates the probability of qualitydeterioration indicating the probability of failing to satisfy the delayquality index value based on the RTT, the BER, and the delay qualityindex value acquired by the acquiring unit 22 (step S4). The estimatingunit 23 estimates the probability of quality deterioration based on theRTT, the BER, and the delay quality index value by use of the equation(3).

The output unit 25 outputs the user proportion, the user delay time, andthe probability of quality deterioration estimated at steps S2 to S5(step S5).

The controlling unit 24 determines whether a communication settingmargin needs adjusting (step S6). The controlling unit 24 calculates theuser communication speed B_(TCP), the communication speed B_(MOD) in themulti-level modulation scheme, and the error rate P_(MOD) in themulti-level modulation scheme by use of the equations (4) to (8). Thecontrolling unit 24 determines whether the communication setting marginneeds adjusting by determining whether B_(EST) is smaller than B_(MOD)and whether at least one of the burst error time or P_(MOD) is smallerthan, for example, a target threshold. Herein, the controlling unit 24may determine whether the user proportion exceeds its target thresholdA′.

If the communication setting margin needs adjusting (YES at step S6),the controlling unit 24 adjusts the communication setting margin (stepS7). If B_(EST) is smaller than B_(MOD), the controlling unit 24determines a new multi-value level M_(i+1), by lowering the multi-valuelevel to lower than the current multi-value level M_(i). Meanwhile, ifat least one of the burst error time or P_(MOD) is smaller than, forexample, a target threshold, the controlling unit 24 determines a newmulti-value level M_(i+1), by raising the multi-value level to higherthan the current multi-value level M_(i). The controlling unit 24selects, from among modulation schemes that can be used in communicationin the optical communication line 16, a modulation scheme correspondingto the determined multi-value level M_(i+1), and changes the modulationscheme to the selected modulation scheme. The controlling unit 24adjusts the communication setting margin by changing the modulationscheme.

Herein, if the user proportion has exceeded A′, the controlling unit 24may change the modulation scheme to a modulation scheme corresponding toa multi-value level that is smaller than the current multi-value levelby one. Meanwhile, if the user proportion is a sufficiently small value,such as 0.1, for example, the controlling unit 24 may change themodulation scheme to a modulation scheme corresponding to a multi-valuelevel that is greater than the current multi-value level by one.

The controlling unit 24 changes the communication setting so that theburst error time does not exceed the RTT. The controlling unit 24performs control so that the burst error time does not exceed the RTT byselecting an FEC setting with a short interleave.

Meanwhile, if the communication setting margin does not need adjustingat step S6, (NO at step S6), the optical transmission device 20terminates the process.

As described above, the optical transmission device 20 estimates anindex value indicating the degree of influence of a burst error oncommunication quality based on quality information concerning the bursterror. Specifically, the optical transmission device 20 estimates theuser proportion, the user delay time, and the probability of qualitydeterioration based on the quality information.

Accordingly, the optical transmission device 20 according to the firstexample embodiment makes it possible to estimate the user proportion,the user delay time, and the probability of quality deterioration, whichenables a communication service provider to grasp the condition ofcommunication quality.

Furthermore, since the use of the optical transmission device 20according to the first example embodiment makes it possible to grasp thedegree of influence on users, a communication service provider canchange a communication setting with the degree of influence on userstaken into consideration. Accordingly, the optical transmission device20 according to the first example embodiment makes it possible tocontrol the communication setting flexibly by, for example, increasingcommunication capacity with the degree of influence on users taken intoconsideration.

The controlling unit 24 adjusts a communication setting margin by use ofthe user proportion. Specifically, the controlling unit 24 changes themodulation scheme by use of the user proportion. The controlling unit 24enables high-speed communication by changing the modulation scheme.Accordingly, the optical transmission device 20 according to the firstexample embodiment makes it possible to provide users with a high-speedcommunication service.

Furthermore, the optical transmission devices 20 and 30 communicate byuse of an ultra-high-speed TCP scheme having higher error resistancethan a typical TCP scheme. As described above, the optical transmissiondevice 20, by use of the ultra-high-speed TCP scheme, can increasecommunication capacity while retaining high user throughput. Moreover,the controlling unit 24 performs control so that a burst error time doesnot exceed RTT and keeps the throughput and communication capacity fromdecreasing by preventing retransmission triggered by RTO. Accordingly,the optical transmission device 20 according to the first exampleembodiment makes it possible to increase communication capacity whileretaining high user throughput.

Second Example Embodiment

Next, a second example embodiment will be described. According to thesecond example embodiment, the process performed by the opticaltransmission device 20 according to the first example embodiment isperformed by a network monitoring device.

<Example of Configuration of Optical Communication System>

With reference to FIG. 8 , an example of a configuration of an opticalcommunication system 200 according to the second example embodiment willbe described. FIG. 8 illustrates an example of a configuration of anoptical communication system according to the second example embodiment.The optical communication system 200 includes a terminal device 10,optical transmission devices 30 and 40, and a network monitoring device50.

The optical communication system 200 includes the network monitoringdevice 50 in addition to the components of the optical communicationsystem 100 according to the first example embodiment. Moreover, in theconfiguration of the optical communication system 200, the opticaltransmission device 20 in the optical communication system 100 accordingto the first example embodiment is replaced by the optical transmissiondevice 40. The configuration of the terminal device 10 and the opticaltransmission device 30 is basically similar to their respectivecounterparts according to the first example embodiment, and thusdescription thereof will be omitted, as appropriate.

The network monitoring device 50 is a device that monitors the entirenetwork in the optical communication system 200. The network monitoringdevice 50 may be referred to as a network management system (NMS). Thenetwork monitoring device 50 is connected to the optical transmissiondevice 20 and communicates with the optical transmission device 40 via anetwork. The network monitoring device 50 monitors the opticaltransmission device 20 and performs control via the optical transmissiondevice 20. Although not illustrated in FIG. 8 , the network monitoringdevice 50 is connected to the optical transmission device 30 as well viaa network and configured to be capable of monitoring the opticaltransmission device 30 and performing control via the opticaltransmission device 30.

<Example of Configuration of Optical Transmission Device>

Next, an example of a configuration of the optical transmission device40 will be described. The optical transmission device 40 corresponds tothe optical transmission device 20 according to the first exampleembodiment. The optical transmission device 40 includes a retransmissionprocess unit 21 and an acquiring unit 41. The retransmission processunit 21 has a configuration similar to the configuration of theretransmission process unit 21 according to the first exampleembodiment, and thus description thereof will be omitted.

The acquiring unit 41 has a configuration basically similar to theconfiguration of the acquiring unit 22 according to the first exampleembodiment. The acquiring unit 41 acquires quality informationconcerning a burst error that occurs in communication in an opticalcommunication line 16. The acquiring unit 41 acquires RTT indicating acommunication round-trip time between the optical transmission devices40 and 30 connected to the optical communication line 16, a burst errortime of a burst error, and BER indicating an error rate in the opticalcommunication line 16. The acquiring unit 41 may further acquire thenumber of users who communicate via the optical communication line 16and SNR in the optical communication line 16. The acquiring unit 41transmits the acquired RTT, burst error time, and BER to the networkmonitoring device 50.

<Example of Configuration of Network Monitoring Device>

Next, an example of a configuration of the network monitoring device 50will be described. The network monitoring device 50 includes anacquiring unit 51, an estimating unit 52, a controlling unit 53, and anoutput unit 54.

The acquiring unit 51 acquires RTT, a burst error time, and BER byreceiving the RTT, the burst error time, and the BER acquired by theacquiring unit 41.

The estimating unit 52 corresponds to the estimating unit 23 accordingto the first example embodiment. The estimating unit 52 has aconfiguration similar to the configuration of the estimating unit 23according to the first example embodiment and executes the processperformed by the estimating unit 23 according to the first exampleembodiment.

The controlling unit 53 corresponds to the controlling unit 24 accordingto the first example embodiment. The controlling unit 53 has aconfiguration similar to the configuration of the controlling unit 24according to the first example embodiment. The controlling unit 53determines whether a communication setting margin needs adjusting basedon the user proportion. In response to determining that a communicationsetting margin needs adjusting, the controlling unit 53 determines thecontents of adjustment to be made to the communication setting margin.

Specifically, the controlling unit 53 determines the modulation schemeof communication in the optical communication line 16 in accordance withthe user proportion estimated by the estimating unit 52. The controllingunit 53 determines an interleave length in FEC so that a burst errortime does not exceed RTT. The controlling unit 53 transmits thedetermined modulation scheme and interleave length to the opticaltransmission device 40 and causes the optical transmission device 40 tochange the modulation scheme and the interleave length.

The output unit 54 corresponds to the output unit 25 according to thefirst example embodiment. The output unit 54 has a configuration similarto the configuration of the output unit 25 according to the firstexample embodiment and executes the process performed by the output unit25 according to the first example embodiment.

<Example of Operation of Network Monitoring Device>

Next, an example of an operation of the network monitoring device willbe described. The operation of the network monitoring device 50 isbasically similar to the example of the operation of the opticaltransmission device 20 according to the first example embodiment andwill thus be described with omissions, as appropriate, with reference toFIG. 7 . The network monitoring device 50 executes the example of theoperation illustrated in FIG. 7 upon the start of the opticaltransmission device 20. In addition, the network monitoring device 50executes the example of the operation illustrated in FIG. 7 when acommunication service provider has made a change to a communicationsetting. Herein, the network monitoring device 50 may start the processat a desired timing while the optical transmission device 40 isstarting.

The acquiring unit 51 acquires, from the optical transmission device 40,RTT indicating a communication round-trip time between the opticaltransmission devices 40 and 30 connected to the optical communicationline 16, a burst error time in which a burst error has occurred, and BERindicating an error rate in the optical communication line 16 (step S1).The acquiring unit 51 acquires the RTT, the burst error time, and theBER by receiving the RTT, the burst error time, and the BER from theoptical transmission device 40.

At step S7, the controlling unit 53 adjusts the communication settingmargin (step S7). When B_(EST) is smaller than B_(MOD), the controllingunit 53 determines a new multi-value level M_(i+1), by lowering themulti-value level to lower than the current multi-value level M_(i).Meanwhile, when at least one of the burst error time or P_(MOD) issmaller than, for example, a target threshold, the controlling unit 53determines a new multi-value level M_(i+1), by raising the multi-valuelevel to higher than the current multi-value level M_(i). Thecontrolling unit 53 selects, from among modulation schemes that can beused in communication in the optical communication line 16, a modulationscheme corresponding to the determined multi-value level M_(i+1). Thecontrolling unit 53 transmits the selected modulation scheme to theoptical transmission device 40 and causes the optical transmissiondevice 40 to execute control of changing the modulation scheme to theselected modulation scheme.

The controlling unit 53 determines an interleave length in FEC so thatthe burst error time does not exceed the RTT. The controlling unit 53transmits the interleave length to the optical transmission device 40and causes the optical transmission device 40 to execute control ofchanging the interleave length to the determined interleave length.

In this manner, even when the network monitoring device 50 executes theprocess that is executed by the optical transmission device 20 accordingto the first example embodiment, advantageous effects similar to thoseaccording to the first example embodiment can be obtained.

Other Example Embodiments

<1> According to the foregoing example embodiments, the opticaltransmission devices 20 and 40 each include a retransmission processunit 21. Alternatively, for example, a relay device (not illustrated)between the optical transmission device 20 or 40 and the terminal device10 may include a retransmission process unit 21. Even with thisconfiguration, advantageous effects similar to those according to theforegoing example embodiments can be obtained.

<2> FIG. 9 illustrates an example of a hardware configuration of thecommunication device 1, the optical transmission devices 20 and 40, andthe network monitoring device 50 (these devices are referred to below asthe communication device 1 and others) described according to theforegoing example embodiments. With reference to FIG. 9 , thecommunication device 1 and others each include a network interface 1201,a processor 1202, and a memory 1203. The network interface 1201 is usedto communicate with another communication device included in an opticalcommunication system, such as an optical transmission device, a terminaldevice, or a network monitoring device.

The processor 1202 reads out software (computer program) from the memory1203 and executes the software. Thus, the processor 1202 performs theprocesses of the communication device 1 and others described withreference to the flowchart according to the foregoing exampleembodiments. The processor 1202 may be, for example, a microprocessor, amicroprocessing unit (MPU), a central processing unit (CPU). Theprocessor 1202 may include a plurality of processors.

The memory 1203 includes a combination of a volatile memory and anon-volatile memory. The memory 1203 may include a storage providedapart from the processor 1202. In this case, the processor 1202 mayaccess the memory 1203 via an I/O interface (not illustrated).

In the example illustrated in FIG. 9 , the memory 1203 is used to storea set of software modules. The processor 1202 reads out the set ofsoftware modules from the memory 1203 and executes the set of softwaremodules. Thus, the processor 1202 can perform the processes of thecommunication device 1 and others described according to the foregoingexample embodiments.

As described with reference to FIG. 9 , each of the processors includedin the communication device 1 and others executes one or more programsincluding a set of instructions for causing a computer to executealgorithms described with reference to the drawings.

In the foregoing examples, a program can be stored and provided to acomputer by use of various types of non-transitory computer-readablemedia.

Non-transitory computer-readable media include various types of tangiblestorage media. Examples of such non-transitory computer-readable mediainclude a magnetic recording medium (e.g., flexible disk, magnetic tape,hard-disk drive), a magneto-optical recording medium (e.g.,magneto-optical disk). Additional examples of non-transitorycomputer-readable media include a CD-ROM (read-only memory), a CD-R, anda CD-R/W. Yet additional examples of non-transitory computer-readablemedia include a semiconductor memory. Examples of semiconductor memoriesinclude a mask ROM, a programmable ROM (PROM), an erasable PROM (EPROM),a flash ROM, or a random-access memory (RAM).

A program may be supplied to a computer also by use of various types oftransitory computer-readable media. Examples of such transitorycomputer-readable media include an electric signal, an optical signal,and an electromagnetic wave. A transitory computer-readable medium cansupply a program to a computer via a wired communication line, such asan electric wire or an optical fiber, or via a wireless communicationline.

It is to be noted that the present disclosure is not limited to theforegoing example embodiments, and modifications can be made asappropriate within the scope that does not depart from the technicalspirit. The present disclosure may be implemented by combining theexample embodiments as appropriate.

A part or the whole of the foregoing example embodiments can also beexpressed as in the following supplementary notes, which are notlimiting.

(Supplementary Note 1)

A communication device comprising:

acquiring means configured to acquire quality information concerning aburst error that has occurred in an optical communication line; and

estimating means configured to estimate a first index value based on thequality information, the first index value indicating a degree ofinfluence of the burst error on communication quality in a firstcommunication device.

(Supplementary Note 2)

The communication device according to Supplementary Note 1, wherein

the first index value includes a user proportion indicating a proportionof the number of users for whom the communication quality deteriorateswith respect to the number of users who communicate via the opticalcommunication line,

the quality information includes a communication round-trip time betweena first optical transmission device and a second optical transmissiondevice each connected to the optical communication line and a bursterror time in which the burst error has occurred, and

the estimating means is configured to estimate the user proportion basedon the communication round-trip time and the burst error time.

(Supplementary Note 3)

The communication device according to Supplementary Note 2, furthercomprising controlling means configured to change a communicationsetting in the optical communication line based on the estimated userproportion.

(Supplementary Note 4)

The communication device according to Supplementary Note 3, wherein thecontrolling means is configured to change a modulation scheme in thecommunication in accordance with the estimated user proportion.

(Supplementary Note 5)

The communication device according to Supplementary Note 4, wherein

the acquiring means is configured to acquire the number of users whocommunicate via the optical communication line and an optical signalquality in the optical communication line, and

the controlling means is configured to change the modulation scheme inthe communication based further on the number of users and the opticalsignal quality.

(Supplementary Note 6)

The communication device according to any one of Supplementary Notes 3to 5, wherein the controlling means is configured to change aninterleave length in an error correction process so that the burst errortime does not exceed the communication round-trip time.

(Supplementary Note 7)

The communication device according to any one of Supplementary Notes 1to 6, wherein

the first index value includes a delay time in the first communicationdevice,

the quality information includes a communication round-trip time betweena first optical transmission device and a second optical transmissiondevice each connected to the optical communication line and an errorrate in the optical communication line, and

the estimating means is configured to estimate the delay time based onthe communication round-trip time and the error rate.

(Supplementary Note 8)

The communication device according to Supplementary Note 7, wherein

the first index value includes a probability of failing to satisfy asecond index value pertaining to a delay time required for communicationin the optical communication line, and

the estimating means is configured to estimate the probability based onthe communication round-trip time, the error rate, and the second indexvalue.

(Supplementary Note 9)

he communication device according to any one of Supplementary Notes 1 to8, further comprising retransmission process means configured to executea retransmission process if an error has occurred in communication inthe optical communication line.

(Supplementary Note 10)

The communication device according to Supplementary Note 9, wherein theretransmission process means is configured to perform the communicationby use of a TCP scheme having higher error resistance than a TCP Renoscheme.

(Supplementary Note 11)

A communication controlling method comprising:

acquiring quality information concerning a burst error that has occurredin an optical communication line; and

estimating a first index value based on the quality information, thefirst index value indicating a degree of influence of the burst error oncommunication quality in a first communication device.

(Supplementary Note 12)

A non-transitory computer-readable medium storing a communicationcontrolling program that causes a computer to execute:

acquiring quality information concerning a burst error that has occurredin an optical communication line; and

estimating a first index value based on the quality information, thefirst index value indicating a degree of influence of the burst error oncommunication quality in a first communication device.

REFERENCE SIGNS LIST

1 COMMUNICATION DEVICE

2, 22, 51 ACQUIRING UNIT

3, 23, 52 ESTIMATING UNIT

10 TERMINAL DEVICE

15 CIRCUIT

16 OPTICAL COMMUNICATION LINE

20, 30, 40 OPTICAL TRANSMISSION DEVICE

21 RETRANSMISSION PROCESS UNIT

24, 53 CONTROLLING UNIT

25, 54 OUTPUT UNIT

41 ACQUIRING UNIT

50 NETWORK MONITORING DEVICE

100, 200 OPTICAL COMMUNICATION SYSTEM

What is claimed is:
 1. A communication device comprising: at least onememory storing instructions; and at least one processor configured toexecute the instructions stored in the memory to: acquire qualityinformation concerning a burst error that has occurred in an opticalcommunication line; and estimate a first index value based on thequality information, the first index value indicating a degree ofinfluence of the burst error on communication quality in a firstcommunication device.
 2. The communication device according to claim 1,wherein the first index value includes a user proportion indicating aproportion of the number of users for whom the communication qualitydeteriorates with respect to the number of users who communicate via theoptical communication line, the quality information includes acommunication round-trip time between a first optical transmissiondevice and a second optical transmission device each connected to theoptical communication line and a burst error time in which the bursterror has occurred, and the processor is configured to execute theinstructions to estimate the user proportion based on the communicationround-trip time and the burst error time.
 3. The communication deviceaccording to claim 2, wherein the processor is further configured toexecute the instructions to change a communication setting in theoptical communication line based on the estimated user proportion. 4.The communication device according to claim 3, wherein the processor isconfigured to execute the instructions to change a modulation scheme inthe communication in accordance with the estimated user proportion. 5.The communication device according to claim 4, wherein the processor isconfigured to execute the instructions to: acquire the number of userswho communicate via the optical communication line and an optical signalquality in the optical communication line, and change the modulationscheme in the communication based further on the number of users and theoptical signal quality.
 6. The communication device according to claim3, wherein the processor is configured to execute the instructions tochange an interleave length in an error correction process so that theburst error time does not exceed the communication round-trip time. 7.The communication device according to claim 1, wherein the first indexvalue includes a delay time in the first communication device, thequality information includes a communication round-trip time between afirst optical transmission device and a second optical transmissiondevice each connected to the optical communication line and an errorrate in the optical communication line, and the processor is configuredto execute the instructions to estimate the delay time based on thecommunication round-trip time and the error rate.
 8. The communicationdevice according to claim 7, wherein the first index value includes aprobability of failing to satisfy a second index value pertaining to adelay time required for communication in the optical communication line,and the processor is configured to execute the instructions to estimatethe probability based on the communication round-trip time, the errorrate, and the second index value.
 9. The communication device accordingto claim 1, wherein the processor is further configured to execute theinstructions to execute a retransmission process if an error hasoccurred in communication in the optical communication line.
 10. Thecommunication device according to claim 9, wherein the processor isconfigured to execute the instructions to perform the communication byuse of a TCP scheme having higher error resistance than a TCP Renoscheme.
 11. A communication controlling method comprising: acquiringquality information concerning a burst error that has occurred in anoptical communication line; and estimating a first index value based onthe quality information, the first index value indicating a degree ofinfluence of the burst error on communication quality in a firstcommunication device.
 12. A non-transitory computer-readable mediumstoring a communication controlling program that causes a computer toexecute: acquiring quality information concerning a burst error that hasoccurred in an optical communication line; and estimating a first indexvalue based on the quality information, the first index value indicatinga degree of influence of the burst error on communication quality in afirst communication device.